1. More common in the lower extremity and usually involves one extremity

2. Cortical hyperostosis ("dripping candle wax")

3. Wavy appearance that flows across and involves joints

E. Pathology

1. Enlarged bony trabeculae

2. Normal haversian systems

F. Treatment

1. Symptomatic treatment of pain

2. Occasionally, correction of contractures by excision of hyperostotic and fibrotic areas

[Figure 1. Melorheostasis. A, AP view of the knee showing periosteal new bone formation on the lateral aspect of the joint. Note the nodular appearance of the heavily ossified bone formation. B, Lateral view of the knee showing the large amount of nodular bone formation arising from the posterior aspect of the distal femur. C, T2-weighted coronal image of the knee showing very low signal nodular masses (corresponding to bone formation) and high signal changes (corresponding to edema) around the nodules.]

II. Massive Osteolysis

A. Definition and demographics

1. Massive osteolysis, also called Gorham disease or vanishing bone disease, is a very rare condition that is characterized by massive resorption of entire segments of bone.

2. Affects both sexes

3. Most common in patients younger than 40 years

B. Etiology/clinical presentation

1. May be related to trauma

2. Abrupt or insidious onset

C. Radiographic appearance

1. Massive osteolysis

2. Progressive lytic bone loss

3. End of the remaining bone is often tapered

4. Often spreads to adjacent bones (crosses joints)

D. Pathology/treatment

1. Begins with numerous vascular channels and ends with fibrosis

2. No effective treatment

III. Gaucher Disease

A. Definition and demographics

1. Gaucher disease is an enzyme deficiency that causes accumulation of glucocerebrosides in the marrow, leading to bone deformities and osteonecrosis.

1. Stress fractures are overuse injuries in which normal bone is subjected to abnormal stresses, resulting in microfractures.

2. Stress fractures occur following repetitive stress in either normal or abnormal bone.

a. Fatigue fracture—Occurs in normal bone, such as in military recruits following marching

[

Figure 3. Coronal CT reconstruction of the proximal femur in a patient with a stress fracture. Note the focal endosteal new bone formation and the periosteal new bone formation on the medial femoral cortex.]

(therefore sometimes called a march fracture).

b. Insufficiency fracture—Occurs in abnormal bone, such as in pagetic patients with femoral shaft bowing.

[Figure 4. Stress fracture. A, Coronal T2-weighted MRI showing high signal in the medullary cavity and on the periosteal surface. B, Axial T2-weighted MRI showing high signal in the medullary cavity and over the posteromedial cortical surface of the tibia.]

b. Linear zone of low signal on T1-weighted images

c. Broad area of increased signal on T2-weighted images

d. When a stress fracture is advanced in clinical course, linear low signal lines representing the fracture may be seen.

1. Neuropathic arthropathy is the destruction of a joint following loss of protective sensation.

[

Figure 5. Neuropathic arthropathy. A, Lateral radiograph of the elbow in a patient with syringomyelia. There are very prominent neuropathic changes with complete destruction of the articular surfaces. B, Lateral radiograph of the ankle in a patient with diabetes mellitus. Note the complete destruction of the articular surfaces with dissolution and fragmentation.]

2. Common locations include the foot, ankle, elbow, and shoulder.

B. Etiology—Disease processes that damage sensory nerves.

1. Diabetes mellitus: affects the foot and ankle

2. Syringomyelia: affects the shoulder and elbow

3. Syphilis: affects the knee

4. Spinal cord tumors: affect the lower extremity joints

C. Clinical presentation

1. Swollen, warm, and erythematous joint with little or no pain

2. Often mimics infection, especially in patients with diabetes

D. Radiographic appearance (Figure 5)

1. Characteristic features: destruction of the joint

2. Initial changes may simulate osteoarthritis

3. Late changes

a. Fragmentation of the joint

b. Subluxation/dislocation

c. Fracture

d. Collapse

E. Pathology

1. Productive/hypertrophic changes secondary to the following spinal cord lesions (generally do not involve the sympathetic nervous system)